1. Field of the Invention
The invention pertains to processes for oxidizing carbohydrate using hypochlorite or chemically similar oxidizing agent with ultraviolet radiation. The oxidation occurs under alkaline conditions.
2. Background of the Invention
The modification of carbohydrate can be divided into two main types: chemical and rheological. Chemical modification generally refers to the substitution of carbohydrate with chemical groups and by means of changing the charge condition of the carbohydrate, gelling behavior or affecting the temperature stability. Rheological modifications are generally used when higher dry matter contents are desirable in a paste, which means decreasing the viscosity by hydrolysis or oxidation. For hydrolysis, enzymes or acids can be used. Oxidation generally involves treating the carbohydrate with bromine, chloride or the corresponding metal hypohalite in an alkaline aqueous medium. For example, oxidation reactions like the treatment of carbohydrate with hypochlorite, such as sodium hypochlorite. Other oxidants like hydrogen peroxide or ammonium persulfate can also be used. Acid conversion is performed by adding acid to hydrolyze the carbohydrate and reduce viscosity.
Regarding starch, for example, oxidation typically involves cleavage of various linkages in the starch molecule. Starch is a glucose polymer, which consists of glucose units linked together by ether bonds at the 1,4 points on the glucose ring to make the linear backbone, with additional branches to the polymer linked at the 1,6 unit on the ring. Oxidation will cleave either of these linkages, reducing molecular weight of the starch molecules. In addition, oxidation can also cleave the glucose ring between the 2, 3 units, and can additionally convert one or both of the resulting aldehyde groups from cleavage to carboxyls. The choice of oxidant, amount of alkali, temperature and reaction time can cause different rates of thinning as well as vary the amount of carboxyls produced in the thinned starch through the oxidation process. Other selective oxidants, like periodate, will only attack certain bonds on starch, with periodates the 2-3 linkage. Acid modification, or thinning, is conducted at relatively low pH and is a more random cleavage, but can continue on to lower viscosities or convert starch to sugars.
The oxidation of starch using chlorine water and actinic light in a carefully controlled reaction having a pH less than 7 is reported in the art for modification resulting in a high carbonyl content end product. The pH is relevant to the success of this process and it is said in the art that decomposition of aldehyde groups occur when the reaction proceeds above of pH of 7. A process is also reported in the art which consists essentially of irradiating polysaccharide with light relatively rich in ultraviolet frequencies in the presence of a compound comprising a nitrile radical. This chemistry relies on the molecular interaction of nitrites with ultraviolet radiation, specifically related to the unique nitrogen electron pair. Nitriles have a different chemical structure than the halogenated oxidants, which react under different mechanisms.
The art is constantly seeking new and more efficient ways to oxidize carbohydrate, particularly methods which reduce chemical costs or reaction time. The present invention concerns oxidation of carbohydrate comprising the treatment of carbohydrate with hypochlorite or chemically similar oxidizing agent and ultraviolet radiation at alkaline conditions. The process provides a more efficient reaction compared to prior art hypochlorite oxidation methods resulting in improved efficiency, reduced chemical demand and a measured reduction in unwanted organic halides.